Cardiotoxicity is a major complication of cancer treatment in protocols involving adriamycin (ADR), radiation, and high doses of cyclophosphamide (cytoxan). Because ADR and radiation are the most frequently used agents in the treatment of cancer, and cytoxan is also used in preparation of patients for bone marrow transplantation, efforts to overcome the dose limiting toxicities of these agents is likely to be beneficial for many cancer patients. The ultimate goal of this research is to develop an antioxidant-based pharmacological intervention for cancer therapy associated cardiac injury. Many studies have been conducted which suggest that both reactive oxygen species (ROS) and reactive nitrogen species (RNS) are produced in vivo by cancer therapeutic agents. However, the contribution of these ROS/RNS to the development of cardiac injury and the mechanism by which ROS/RNS mediates cardiac toxicity is unclear. We hypothesize that removal of superoxide radicals in the mitochondria is the critical step in protection against ROS/RNS-induced cardiac toxicity and tumor necrosis factor (TNF)-modulated cardiac injury during cancer therapy. To test this hypothesis, expression of MnSOD and GPX in the mitochondria of heart tissue will be elevated by transgenic manipulations, and the level of inducible nitric oxide synthase (iNOS) will be manipulated by targeted gene disruptions. The effects of the anticancer agents, ADR, cytoxan, and ionizing radiation on heart tissue will be examined in transgenic mice expressing increased individual or combined MnSOD (MnSOD-Tg) and mitochondrial GPX (mGPX-Tg) activity as well as in mice deficient in the inducible form of nitric oxide synthase (iNOS-KO). Cardiac injury will be assessed by determining the production of oxidatively damaged products, the respiratory function of isolated mitochondria, the formation of ultrastructural and histopathological lesions, as well as the extent of cardiomyocyte injury or cell death. The role of TNF in therapy-induced cardiac toxicity will be examined in TNF receptors knockout mice (TNFRs-KO) that express the human MnSOD transgenes (MnSOD-Tg/TNFRs-KO) using the same molecular, biochemical, and pathological end points. The results obtained from this study should demonstrate clearly how ROS/RNS contribute to cardiac toxicity and suggest potential points for pharmacological intervention of cardiac injury during cancer treatments.